Heat shock protein 70B' (HSP70B') expression and release in response to human oxidized low density lipoprotein immune complexes in macrophages

Pharmacological Modulation of the Unfolded Protein Response as a Therapeutic Approach in Cutaneous T-Cell Lymphoma

Cutaneous T-cell lymphoma (CTCL) is a rare T-cell malignancy characterized by inflamed and painful rash-like skin lesions that may affect large portions of the body's surface. Patients experience recurrent infections due to a compromised skin barrier and generalized immunodeficiency resulting from a dominant Th2 immune phenotype of CTCL cells. Given the role of the unfolded protein response (UPR) in normal and malignant T-cell development, we investigated the impact of UPR-inducing drugs on the viability, transcriptional networks, and Th2 phenotype of CTCL. We found that CTCL cells were >5-fold more sensitive to the proteasome inhibitor bortezomib (Btz) and exhibited a distinct signaling and transcriptional response compared to normal CD4+ cells. The CTCL response was dominated by the induction of the HSP70 family member HSPA6 (HSP70B') and, to a lesser extent, HSPA5 (BiP/GRP78). To understand the significance of these two factors, we used a novel isoform selective small-molecule inhibitor of HSPA5/6 (JG-023). JG-023 induced pro-apoptotic UPR signaling and enhanced the cytotoxic effects of proteasome inhibitors and other UPR-inducing drugs in CTCL but not normal T cells. Interestingly, JG-023 also selectively suppressed the production of Th2 cytokines in CTCL and normal CD4+ T cells. Conditioned media (CM) from CTCL were immunosuppressive to normal T cells through an IL-10-dependent mechanism. This immunosuppression could be reversed by JG-023, other HSP70 inhibitors, Btz, and combinations of these UPR-targeted drugs. Our study points to the importance of the UPR in the pathology of CTCL and demonstrates the potential of proteasome and targeted HSPA5/6 inhibitors for therapy.

Identification and Characterization of Prognostic Macrophage Subpopulations for Human Esophageal Carcinoma

AIMS

The aim of the present study was to investigate the relationship between the cellular ecosystem and the progression of esophageal carcinoma (ESCA) based on the evolution of macrophages and to analyze the potential of using macrophages as a new therapeutic approach in ESCA treatment.

BACKGROUND

Macrophage-based immunotherapy could be used for treating ESCA patients, but its clinical application is limited by the intra-tumor heterogeneity of macrophages.

OBJECTIVE

The objective of this study was to analyze the diversity, differentiation trajectory, and intercellular communication of macrophages in ESCA and its prognostic significance.

METHODS

Single-cell RNA sequencing (scRNA-seq) data in the GSE154763 dataset were downloaded from Gene Expression Omnibus (GEO) to identify cell clusters and annotate cell types using the Seurat R package. The scRNA-seq profiles of macrophages were extracted, and cluster analysis was performed to identify macrophage subsets. The differentiation trajectories of macrophage subgroups were visualized employing Monocle2. Finally, ligand-receptor pairs and communication intensity among the classified subgroups were analyzed using Cell Chat.

RESULTS

A total of 8 cell types were identified between ESCA tissues and paracancer tissues. The most abundant macrophages in ESCA tissues were further divided into 5 cell clusters. Compared with the normal tissues, the proportion of HSPA6+ macrophages in ESCA tissues increased the most, and the number of ligand-receptor pairs that mediated the communication of HSPA6+ macrophages with mast cells and monocytes also increased significantly. More importantly, a high proportion of HSPA6+ macrophages was inversely correlated with the survival outcomes for ESCA patients.

CONCLUSIONS

This study analyzed the diversity, distribution and differentiation trajectory of macrophages in ESCA tissues at single-cell level and classified a prognostic macrophage subtype (HSPA6+ macrophages) of ESCA, providing a theoretical basis for macrophage-targeted therapy in ESCA.

Targeting Oxidative Stress Involved in Endometriosis and Its Pain

Endometriosis is a common gynecological disorder seen in women and is characterized by chronic pelvic pain and infertility. This disorder is becoming more prevalent with increased morbidity. The etiology of endometriosis remains to be fully elucidated, which will lead to improved therapeutic options. In this review, we will evaluate the biochemical mechanisms leading to oxidative stress and their implication in the pathophysiology of endometriosis, as well as potential treatments that target these processes. A comprehensive exploration of previous research revealed that endometriosis is associated with elevated reactive oxygen species and oxidation products, decreased antioxidants and detoxification enzymes, and dysregulated iron metabolism. High levels of oxidative stress contributed to inflammation, extracellular matrix degradation, angiogenesis, and cell proliferation, which may explain its role in endometriosis. Endometriosis-associated pain was attributed to neurogenic inflammation and a feed-forward mechanism involving macrophages, pro-inflammatory cytokines, and pain-inducing prostaglandins. N-acetylcysteine, curcumin, melatonin, and combined vitamin C and E supplementation displayed promising results for the treatment of endometriosis, but further research is needed for their use in this population.

Prediction of Mechanosensitive Genes in Vascular Endothelial Cells Under High Wall Shear Stress

Objective: The vulnerability of atherosclerotic plaques is among the leading cause of ischemic stroke. High wall shear stress (WSS) promotes the instability of atherosclerotic plaques by directly imparting mechanical stimuli, but the specific mechanisms remain unclear. We speculate that modulation of mechanosensitive genes may play a vital role in accelerating the development of plaques. The purpose of this study was to find mechanosensitive genes in vascular endothelial cells (ECs) through combining microarray data with bioinformatics technology and further explore the underlying dynamics–related mechanisms that cause the progression and destabilization of atherosclerotic plaques.

Methods: Microarray data sets for human vascular ECs under high and normal WSS were retrieved from the Gene Expression Omnibus (GEO) database. Differentially expressed genes (DEGs) were identified through the R language. The performance of enrichment analysis and protein–protein interaction (PPI) network presented the biological function and signaling pathways of the DEGs. Hub genes were identified based on the PPI network and validated by GEO data sets. Predicted transcription factor (TF) genes and miRNAs interaction with potential mechanosensitive genes were identified by NetworkAnalyst.

Results: A total of 260 DEGs, 121 upregulated and 139 downregulated genes, were screened between high and normal WSS from GSE23289. A total of 10 hub genes and four cluster modules were filtered out based on the PPI network. The enrichment analysis showed that the biological functions of the hub genes were mainly involved in responses to unfolded protein and topologically incorrect protein, and t to endoplasmic reticulum stress. The significant pathways associated with the hub genes were those of protein processing in the endoplasmic reticulum, antigen processing, and presentation. Three out of the 10 hub genes, namely, activated transcription factor 3 (ATF3), heat shock protein family A (Hsp70) member 6 (HSPA6), and dual specificity phosphatase 1 (DUSP1, also known as CL100, HVH1, MKP-1, PTPN10), were verified in GSE13712. The expression of DUSP1 was higher in the senescent cell under high WSS than that of the young cell. The TF–miRNA–mechanosensitive gene coregulatory network was constructed.

Conclusion: In this work, we identified three hub genes, ATF3, HSPA6, and DUSP1, as the potential mechanosensitive genes in the human blood vessels. DUSP1 was confirmed to be associated with the senescence of vascular ECs. Therefore, these three mechanosensitive genes may have emerged as potential novel targets for the prediction and prevention of ischemic stroke. Furthermore, the TF–miRNA–mechanosensitive genes coregulatory network reveals an underlying regulatory mechanism and the pathways to control disease progression.

Roles of Extracellular HSPs as Biomarkers in Immune Surveillance and Immune Evasion

Extracellular heat shock proteins (ex-HSPs) have been found in exosomes, oncosomes, membrane surfaces, as well as free HSP in cancer and various pathological conditions, also known as alarmins. Such ex-HSPs include HSP90 (α, β, Gp96, Trap1), HSP70, and large and small HSPs. Production of HSPs is coordinately induced by heat shock factor 1 (HSF1) and hypoxia-inducible factor 1 (HIF-1), while matrix metalloproteinase 3 (MMP-3) and heterochromatin protein 1 are novel inducers of HSPs. Oncosomes released by tumor cells are a major aspect of the resistance-associated secretory phenotype (RASP) by which immune evasion can be established. The concepts of RASP are: (i) releases of ex-HSP and HSP-rich oncosomes are essential in RASP, by which molecular co-transfer of HSPs with oncogenic factors to recipient cells can promote cancer progression and resistance against stresses such as hypoxia, radiation, drugs, and immune systems; (ii) RASP of tumor cells can eject anticancer drugs, targeted therapeutics, and immune checkpoint inhibitors with oncosomes; (iii) cytotoxic lipids can be also released from tumor cells as RASP. ex-HSP and membrane-surface HSP (mHSP) play immunostimulatory roles recognized by CD91+ scavenger receptor expressed by endothelial cells-1 (SREC-1)+ Toll-like receptors (TLRs)+ antigen-presenting cells, leading to antigen cross-presentation and T cell cross-priming, as well as by CD94+ natural killer cells, leading to tumor cytolysis. On the other hand, ex-HSP/CD91 signaling in cancer cells promotes cancer progression. HSPs in body fluids are potential biomarkers detectable by liquid biopsies in cancers and tissue-damaged diseases. HSP-based vaccines, inhibitors, and RNAi therapeutics are also reviewed.

Heat Shock Proteins and Cancer

Heat shock proteins (HSPs) constitute a large family of proteins involved in protein folding and maturation whose expression is induced by heat shock or other stressors. The major groups are classified based on their molecular weights and include HSP27, HSP40, HSP60, HSP70, HSP90, and large HSPs. HSPs play a significant role in cellular proliferation, differentiation, and carcinogenesis. In this article we comprehensively review the roles of major HSPs in cancer biology and pharmacology. HSPs are thought to play significant roles in the molecular mechanisms leading to cancer development and metastasis. HSPs may also have potential clinical uses as biomarkers for cancer diagnosis, for assessing disease progression, or as therapeutic targets for cancer therapy.

Endothelial nitric oxide synthase induces heat shock protein HSPA6 (HSP70B') in human arterial smooth muscle cells

Endothelial nitric oxide synthase (eNOS) is the major source of nitric oxide (NO) production in blood vessels. One of the pleitropic functions of eNOS derived NO is to inhibit vascular smooth muscle cell proliferation in the blood vessel wall, and whose dysfunction is a primary cause of atherosclerosis and restenosis. In this study there was an interest in examining the gene profile of eNOS adenoviral (Ad-eNOS) transduced human coronary artery smooth muscle cells (HCASMC) to further understand the eNOS inhibitory effect on smooth muscle cell proliferation. To this aim a whole genome wide analysis of eNOS transduced HCASMCs was performed. A total of 19 genes were up regulated, and 31 genes down regulated in Ad-eNOS transduced HCASMCs compared to cells treated with an empty adenovirus. Noticeably, a cluster of HSP70 gene family members was amongst the genes up regulated. Quantitative PCR confirmed that transcripts for HSPA1A (HSP70A), HSPA1B (HSP70B) and HSPA6 (HSP70B') were elevated 2, 1.7 and 14-fold respectively in Ad-eNOS treated cells. The novel gene HSPA6 was further explored as a potential mediator of eNOS signaling in HCASMC. Immunoblotting showed that HSPA6 protein was induced by Ade-NOS. To functionally examine the effect of HSPA6 on SMCs, an adenovirus harboring the HSPA6 gene under the control of a constitutive promoter was generated. Transduction of HCASMCs with Ad-HSPA6 inhibited SMC proliferation at 3 and 6 days post serum growth stimulation, and paralleled the Ad-eNOS inhibition of SMC growth. The identification in this study that HSPA6 overexpression inhibits SMC proliferation coupled with the recent finding that inhibition of HSP90 has a similar effect, progresses the field of targeting HSPs for vascular repair.

Accelerated vascular disease in systemic lupus erythematosus: role of macrophage

Atherosclerosis is a chronic inflammatory condition that is considered a major cause of death worldwide. Striking phenomena of atherosclerosis associated with systemic lupus erythematosus (SLE) is its high incidence in young patients. Macrophages are heterogeneous cells that differentiate from hematopoietic progenitors and reside in different tissues to preserve tissue integrity. Macrophages scavenge modified lipids and play a major role in the development of atherosclerosis. When activated, macrophages secret inflammatory cytokines. This activation triggers apoptosis of cells in the vicinity of macrophages. As such, macrophages play a significant role in tissue remodeling including atherosclerotic plaque formation and rupture. In spite of studies carried on identifying the role of macrophages in atherosclerosis, this role has not been studied thoroughly in SLE-associated atherosclerosis. In this review, we address factors released by macrophages as well as extrinsic factors that may control macrophage behavior and their effect on accelerated development of atherosclerosis in SLE.

Stress-induced localization of HSPA6 (HSP70B') and HSPA1A (HSP70-1) proteins to centrioles in human neuronal cells

The localization of yellow fluorescent protein (YFP)-tagged HSP70 proteins was employed to identify stress-sensitive sites in human neurons following temperature elevation. Stable lines of human SH-SY5Y neuronal cells were established that expressed YFP-tagged protein products of the human inducible HSP70 genes HSPA6 (HSP70B') and HSPA1A (HSP70-1). Following a brief period of thermal stress, YFP-tagged HSPA6 and HSPA1A rapidly appeared at centrioles in the cytoplasm of human neuronal cells, with HSPA6 demonstrating a more prolonged signal compared to HSPA1A. Each centriole is composed of a distal end and a proximal end, the latter linking the centriole doublet. The YFP-tagged HSP70 proteins targeted the proximal end of centrioles (identified by γ-tubulin marker) rather than the distal end (centrin marker). Centrioles play key roles in cellular polarity and migration during neuronal differentiation. The proximal end of the centriole, which is involved in centriole stabilization, may be stress-sensitive in post-mitotic, differentiating human neurons.

Oxidized LDL and AGE-LDL in circulating immune complexes strongly predict progression of carotid artery IMT in type 1 diabetes

OBJECTIVE

Over 90% of modified LDL in circulation is associated to specific antibodies circulating as part of immune complexes (IC); however, few studies have examined their relationship with cardiovascular disease.

METHODS

We report the relationship between circulating concentrations of IC of oxidized LDL (oxLDL-IC), malondialdehyde-LDL (MDA-LDL-IC) and advanced glycation end products-LDL (AGE-LDL-IC) and progression of atherosclerosis over a 12 year period in 467 individuals with type 1 diabetes who participated in the Diabetes Control and Complications Trial (DCCT) and the Epidemiology of Diabetes Interventions and Complications (EDIC) study. OxLDL-IC, AGE-LDL-IC and MDA-LDL-IC levels were measured at DCCT closeout. Internal carotid intima-medial thickness (IMT) was measured at EDIC follow-up years 1, 6 and 12.

RESULTS

OxLDL-IC, AGE-LDL-IC and MDA-LDL-IC levels were significantly correlated with age, lipid levels, blood pressure levels and albumin excretion rates. Levels of oxLDL, AGE-LDL and MDA-LDL in isolated LDL-IC were highly inter-correlated (r = 0.66-0.84, P < 0.0001). After adjusting for cardiovascular risk factors individuals in the upper quartile of oxLDL-IC had a 2.98-fold increased odds (CI: 1.34, 6.62) of having IMT ≥ 1.00 mm and had a 5.13-fold increased odds (CI: 1.98, 13.3) of having significant IMT progression, relative to those in the lowest quartile. Parallel odds ratios for AGE-LDL-IC were 2.95 (CI: 1.37, 6.34) and 3.50 (CI: 1.38, 8.86), while results for MDA-LDL-IC were 1.76 (0.87, 3.56) and 2.86 (1.20, 6.81).

CONCLUSION

Our study indicates that high levels of oxLDL-IC and AGE-LDL-IC are important predictors of carotid intima-medial thickening in patients with type 1 diabetes.

Evidence on the pathogenic role of auto-antibodies in acute cardiovascular diseases

Atherothrombosis is the major determinant of acute ischaemic cardiovascular events, such as myocardial infarction and stroke. Inflammatory processes have been linked to all phases of atherogenesis In particular, the identification of autoimmunity mediators in the complex microenvironment of chronic inflammation has become the focus of attention in both early and advanced atherogenic processes. Auto-antibodies against self-molecules or new epitopes generated by oxidative processes infiltrate atherosclerotic plaques and were shown to modulate the activity of immune cells by binding various types of receptors. However, despite mounting evidence for a pathophysiological role of autoantibodies in atherothrombosis, the clinical relevance for circulating autoantibodies in cardiovascular outcomes is still debated. This review aims at illustrating the mechanisms by which different types of autoantibodies might either promote or repress atherothrombosis and to discuss the clinical studies assessing the role of auto-antibodies as prognostic biomarkers of plaque vulnerability.

Differential regulation of acid sphingomyelinase in macrophages stimulated with oxidized low-density lipoprotein (LDL) and oxidized LDL immune complexes: role in phagocytosis and cytokine release

Oxidized low-density lipoprotein (oxLDL) and oxLDL-containing immune complexes (oxLDL-IC) contribute to the formation of lipid-laden macrophages (foam cells). Fcγ receptors mediate uptake of oxLDL-IC, whereas scavenger receptors internalize oxLDL. We have previously reported that oxLDL-IC, but not free oxLDL, activate macrophages and prolong their survival. Sphingomyelin is a major constituent of cell membranes and lipoprotein particles and acid sphingomyelinase (ASMase) hydrolyses sphingomyelin to generate the bioactive lipid ceramide. ASMase exists in two forms: lysosomal (L-ASMase) and secretory (S-ASMase). In this study we examined whether oxLDL and oxLDL-IC regulate ASMase differently, and whether ASMase mediates monocyte/macrophage activation and cytokine release. The oxLDL-IC, but not oxLDL, induced early and consistent release of catalytically active S-ASMase. The oxLDL-IC also consistently stimulated L-ASMase activity, whereas oxLDL induced a rapid transient increase in L-ASMase activity before it steadily declined below baseline. Prolonged exposure to oxLDL increased L-ASMase activity; however, activity remained significantly lower than that induced by oxLDL-IC. Further studies were aimed at defining the function of the activated ASMase. In response to oxLDL-IC, heat-shock protein 70B' (HSP70B') was up-regulated and localized with redistributed ASMase in the endosomal compartment outside the lysosome. Treatment with oxLDL-IC induced the formation and release of HSP70-containing and IL-1β-containing exosomes via an ASMase-dependent mechanism. Taken together, the results suggest that oxLDL and oxLDL-IC differentially regulate ASMase activity, and the pro-inflammatory responses to oxLDL-IC are mediated by prolonged activation of ASMase. These findings may contribute to increased understanding of mechanisms mediating macrophage involvement in atherosclerosis.

Uptake and protein targeting of fluorescent oxidized phospholipids in cultured RAW 264.7 macrophages

The truncated phospholipids 1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphocholine (POVPC) and 1-palmitoyl-2-glutaroyl-sn-glycero-3-phosphocholine (PGPC) are oxidation products of 1-palmitoyl-2-arachidonoyl phosphatidylcholine. Depending on concentration and the extent of modification, these compounds induce growth and death, differentiation and inflammation of vascular cells thus playing a role in the development of atherosclerosis. Here we describe the import of fluorescent POVPC and PGPC analogs into cultured RAW 264.7 macrophages and the identification of their primary protein targets. We found that the fluorescent oxidized phospholipids were rapidly taken up by the cells. The cellular target sites depended on the chemical reactivity of these compounds but not on the donor (aqueous lipid suspension, albumin or LDL). The great differences in cellular uptake of PGPC and POVPC are a direct consequence of the subtle structural differences between both molecules. The former compound (carboxyl lipid) can only physically interact with the molecules in its immediate vicinity. In contrast, the aldehydo-lipid covalently reacts with free amino groups of proteins by forming covalent Schiff bases, and thus becomes trapped in the cell surface. Despite covalent binding, POVPC is exchangeable between (lipo)proteins and cells, since imines are subject to proton-catalyzed base exchange. Protein targeting by POVPC is a selective process since only a limited subfraction of the total proteome was labeled by the fluorescent aldehydo-phospholipid. Chemically stabilized lipid–protein conjugates were identified by MS/MS. The respective proteins are involved in apoptosis, stress response, lipid metabolism and transport. The identified target proteins may be considered primary signaling platforms of the oxidized phospholipid.

The Pathogenic Role of the Adaptive Immune Response to Modified LDL in Diabetes

The main causes of morbidity and mortality in diabetes are macro and microvascular complications, including atherosclerosis, nephropathy, and retinopathy. As the definition of atherosclerosis as a chronic inflammatory disease became widely accepted, it became important to define the triggers of vascular inflammation. Oxidative and other modifications of lipids and lipoproteins emerged as major pathogenic factors in atherosclerosis. Modified forms of LDL (mLDL) are pro-inflammatory by themselves, but, in addition, mLDLs including oxidized, malondialdehyde (MDA)-modified, and advanced glycation end (AGE)-product-modified LDL induce autoimmune responses in humans. The autoimmune response involves T cells in the arterial wall and synthesis of IgG antibodies. The IgG auto-antibodies that react with mLDLs generate immune complexes (IC) both intra and extravascularly, and those IC activate the complement system as well as phagocytic cells via the ligation of Fcγ receptors. In vitro studies proved that the pro-inflammatory activity of IC containing mLDL (mLDL-IC) is several-fold higher than that of the modified LDL molecules. Clinical studies support the pathogenic role of mLDL-IC in the development of macrovascular disease patients with diabetes. In type 1 diabetes, high levels of oxidized and AGE-LDL in IC were associated with internal carotid intima-media thickening and coronary calcification. In type 2 diabetes, high levels of MDA-LDL in IC predicted the occurrence of myocardial infarction. There is also evidence that mLDL-IC are involved in the pathogenesis of diabetic nephropathy and retinopathy. The pathogenic role of mLDL-IC is not unique to diabetic patients, because those IC are also detected in non-diabetic individuals. But mLDL-IC are likely to reach higher concentrations and have a more prominent pathogenic role in diabetes due to increased antigenic load secondary to high oxidative stress and to enhanced autoimmune responses in type 1 diabetes.

Rescuing of deficient killing and phagocytic activities of macrophages derived from non-obese diabetic mice by treatment with geldanamycin or heat shock: potential clinical implications

Diabetes mellitus type 1 (DMT1) is an autoimmune disease characterized by the destruction of insulin-producing cells in the pancreas. Diabetic patients are more susceptible to recurrent and uncontrolled infections, with worse prognoses than in healthy individuals. Macrophages (MΦs) derived from DMT1 individuals have compromised mounting of inflammatory and immune responses. The mechanisms responsible for these alterations remain unknown. It has been shown that the presence of extra- and intracellular heat shock proteins (hsp) positively modulates immune cell function. Using naive MΦs derived from non-obese diabetic (NOD) mice, a well-established mouse model for DMT1, we demonstrate that heat shock (HS) as well as treatment with geldanamycin (GA), significantly improves diabetic MΦ activation, resulting in increased phagocytosis and killing of bacteria. Induction of HS did not affect the aberrant NOD-MΦ cytokine profile, which is characterized by elevated IL-10 levels and normal tumor necrosis factor alpha. Our observations were consistent at pre-diabetic (normal random blood glucose) and diabetic (random blood glucose greater than 250 mg/dl) stages, suggesting that HS and GA treatment may compensate for intrinsic genetic alterations present in diabetic cells regardless of the stage of the disease. The mechanisms associated to this phenomenon are unknown, but they may likely be associated with the induction of hsp expression, a common factor between HS and GA treatment. Our results may open a new field for non-classical function of hsp and indicate that hsp expression may be used as a part of therapeutic approaches for the treatment of complications associated with DMT1 as well as other autoimmune diseases.

Differential trafficking of oxidized LDL and oxidized LDL immune complexes in macrophages: impact on oxidative stress

Background

Oxidized low-density lipoproteins (oxLDL) and oxLDL-containing immune complexes (oxLDL-IC) contribute to formation of lipid-laden macrophages (foam cells). It has been shown that oxLDL-IC are considerably more efficient than oxLDL in induction of foam cell formation, inflammatory cytokines secretion, and cell survival promotion. Whereas oxLDL is taken up by several scavenger receptors, oxLDL-IC are predominantly internalized through the FCγ receptor I (FCγ RI). This study examined differences in intracellular trafficking of lipid and apolipoprotein moieties of oxLDL and oxLDL-IC and the impact on oxidative stress.

Methodology/Findings

Fluorescently labeled lipid and protein moieties of oxLDL co-localized within endosomal and lysosomal compartments in U937 human monocytic cells. In contrast, the lipid moiety of oxLDL-IC was detected in the endosomal compartment, whereas its apolipoprotein moiety advanced to the lysosomal compartment. Cells treated with oxLDL-IC prior to oxLDL demonstrated co-localization of internalized lipid moieties from both oxLDL and oxLDL-IC in the endosomal compartment. This sequential treatment likely inhibited oxLDL lipid moieties from trafficking to the lysosomal compartment. In RAW 264.7 macrophages, oxLDL-IC but not oxLDL induced GFP-tagged heat shock protein 70 (HSP70) and HSP70B', which co-localized with the lipid moiety of oxLDL-IC in the endosomal compartment. This suggests that HSP70 family members might prevent the degradation of the internalized lipid moiety of oxLDL-IC by delaying its advancement to the lysosome. The data also showed that mitochondrial membrane potential was decreased and generation of reactive oxygen and nitrogen species was increased in U937 cell treated with oxLDL compared to oxLDL-IC.

Conclusions/Significance

Findings suggest that lipid and apolipoprotein moieties of oxLDL-IC traffic to separate cellular compartments, and that HSP70/70B' might sequester the lipid moiety of oxLDL-IC in the endosomal compartment. This mechanism could ultimately influence macrophage function and survival. Furthermore, oxLDL-IC might regulate the intracellular trafficking of free oxLDL possibly through the induction of HSP70/70B'.